Summary

The CLR includes a default host that enables you to use application configuration files to specify which version and build type of the CLR to use and in which garbage collection mode to run. If you don't need to customize the settings for domain-neutral code and if you don't require any other features of the CLR hosting API, using the default host can save you time.

The configuration file used to customize the default CLR host enables you to list more than one version of the CLR with which to run the application. If multiple versions are listed, the order of the versions in the list determines their priority. However, it's always safest to list only the version of the CLR your application was built with because that's the version that offers the most predictable behavior at run time. If you choose to list additional versions, make sure you've completed sufficient testing to ensure that the other versions are backward compatible from the perspective of your application.

Finally, if you've determined that your application can run on a machine that has only .NET Framework 1.0 installed on it, you must include extra statements in your configuration file to upgrade these references manually because the CLR that shipped with .NET Framework 1.0 does not automatically upgrade all references to the .NET Framework assemblies to match the CLR.